From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:56696) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QeqeJ-00057e-12 for qemu-devel@nongnu.org; Thu, 07 Jul 2011 11:37:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QeqeG-0001Ze-SX for qemu-devel@nongnu.org; Thu, 07 Jul 2011 11:37:54 -0400 Received: from mail-gw0-f45.google.com ([74.125.83.45]:62698) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QeqeG-0001ZZ-H3 for qemu-devel@nongnu.org; Thu, 07 Jul 2011 11:37:52 -0400 Received: by gwb19 with SMTP id 19so509765gwb.4 for ; Thu, 07 Jul 2011 08:37:51 -0700 (PDT) Message-ID: <4E15D2CD.6040204@codemonkey.ws> Date: Thu, 07 Jul 2011 10:37:49 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <4E148776.4000805@redhat.com> <4E1497C6.4060505@codemonkey.ws> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] migration: new sections and backward compatibility. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: jes sorensen , Juan Quintela , "qemu-devel@nongnu.org" , Gerd Hoffmann On 07/07/2011 04:23 AM, Markus Armbruster wrote: > Anthony Liguori writes: > >> On 07/06/2011 11:04 AM, Gerd Hoffmann wrote: >>> Hi folks, >>> >>> We'll need to figure a sane way to handle migration to older versions >>> with new sections, i.e. devices which used to not save state before do now. >>> >>> We already have one case in tree: usb. qemu 0.14 saves state for usb-hid >>> devices and the usb-hub, whereas qemu 0.13 and older don't. You can't >>> migrate a vm with a usb-tablet from 0.14 to 0.13 because of that even if >>> you use -M pc-0.13. >> >> Because if you did migrate, you would actively break the guest during >> migration. So why is this a problem? >> >> This comes up a lot. We shouldn't enable migration if we know the >> guest is going to break during migration. That's a feature, not a >> bug. > > Not so fast :) > > I agree that throwing away unrecognized migration data is unsafe, and > should not be done. Now let me present my little problem. > > I'm working on making migration preserve "tray status": open/closed, > locked/unlocked. > > For ide-cd, I can stick a subsection "ide_drive/tray_state" into section > "ide_drive". Needed only if the tray is open or locked. This gives > users a chance to migrate to older versions, and is perfectly safe. > > scsi-cd doesn't have a section, yet. What now? Is that because 'scsi-cd' doesn't need a section or because it hasn't been implemented yet? Regards, Anthony Liguori >